Base station apparatus, terminal apparatus, and communication method

ABSTRACT

There are provided a base station apparatus, a terminal apparatus, and a communication method which are capable of realizing a LTE-A system with improved throughput by performing a CA technology including an unlicensed band while suppressing interference from an existing system. A base station apparatus according to the present invention is a base station apparatus which is included in a communication system that applies a communication scheme applied to a first frequency band capable of being used as a dedicated frequency band to a second frequency band different from the first frequency band and is capable of communicating with a terminal apparatus by using the second frequency band and the second frequency band. The base station apparatus synchronizes a frame number of a frame of a first signal transmitted using the first frequency band with a frame number of a frame of a second signal irrespective of whether or not the second signal transmitted using the second frequency band is transmitted.

TECHNICAL FIELD

The present invention relates to a base station apparatus, a terminalapparatus, and a communication method.

BACKGROUND ART

The standardization of a Long Term Evolution (LTE) system which is awireless communication system of 3.9G mobile phones has been completed,and the standardization of LTE-Advanced (LTE-A) (also referred to asIMT-A) system which is an enhancement of the LTE system as one of 4Gwireless communication systems is being currently performed.

In the LTE-A system (from LTE Rel. 10 on), a carrier aggregation (CA)technology of using one system band of the LTE system as a componentcarrier (CC) (also referred to as a serving cell) and simultaneouslyusing a plurality of CCs has been adopted. In a case where CA isperformed, one CC is used as a primary cell (Pcell) capable of realizingall functions, and other CCs are used as a secondary cell (Scell).

Reserving frequency resources while coping with a rapid increase in datatraffic in the LTE system is an important issue. A frequency bandassumed for the LTE system so far has been a frequency band referred toas a so-called licensed band permitted for use by a country or alocality in which a radio communication operator provides services, andhas limitations in an available frequency band.

Thus, the provision of an LTE system that uses a frequency band referredto as a so-called unlicensed band which does not require permission foruse by a country or a locality has been recently discussed (see NPL 1).The CA technology adopted by the LTE-A system is also applied to anunlicensed band, and thus, it is expected that the LTE-A system will beable to cope with a rapid increase in data traffic with high efficiency.

CITATION LIST Non Patent Literature

NPL 1: RP-140259, “Study on Licensed-Assisted Access using LTE,” 3GPPTSGRAN Meeting #63, March 2014.

SUMMARY OF INVENTION Technical Problem

However, in an unlicensed band, as represented by an IEEE 802.11 system,communication is likely to be performed by a radio access technology(RAT) different from LTE. Accordingly, if the LTE-A system simplyapplies the CA technology to the unlicensed band, throughput maydeteriorate due to interference from another system.

The present invention has been made in view of such circumstances, andit is an object of the invention to provide a base station apparatus, aterminal apparatus, and a communication method which are capable ofrealizing a LTE-A system with improved throughput by implementing a CAtechnology including an unlicensed band while suppressing interferencefrom an existing system.

Solution to Problem

A base station apparatus, a terminal apparatus, and a communicationmethod according to the present invention for solving theabove-described problems are as follows.

(1) That is, a base station apparatus according to the present inventionis a base station apparatus which is included in a communication systemthat applies a communication scheme applied to a first frequency bandcapable of being used as a dedicated frequency band to a secondfrequency band different from the first frequency band and is capable ofcommunicating with a terminal apparatus by using the second frequencyband and the second frequency band. The base station apparatussynchronizes a frame number of a frame of a first signal transmittedusing the first frequency band with a frame number of a frame of asecond signal irrespective of whether or not the second signaltransmitted using the second frequency band is transmitted.

(2) In accordance with the base station apparatus according to thepresent invention, in the base station apparatus described in (1), atleast signal null periods are included in the frame of the second signaltransmitted using the second frequency band, and a frame length of asignal frame included in the frame of the second signal transmittedusing the second frequency band is less than a frame length of a signalframe included in the frame of the first signal transmitted using thefirst frequency band.

(3) In accordance with the base station apparatus according to thepresent invention, in the base station apparatus described in (2), aplurality of frequency bands is included in the second frequency band,and the frame of the second signal is constituted depending onperformance of the plurality of frequency bands.

(4) In accordance with the base station apparatus according to thepresent invention, in the base station apparatus described in (3),priority levels for applying the communication scheme are assigned tothe plurality of frequency bands.

(5) In accordance with the base station apparatus according to thepresent invention, in the base station apparatus described in any one of(2) to (4), a utilization status of the second frequency band ismeasured during at least a part of null periods, a frame structure ofthe second signal is changed on the basis of the measurement result, andinformation indicating the change of the frame structure is signaled tothe terminal apparatus.

(6) In accordance with the base station apparatus according to thepresent invention, in the base station apparatus described in any one of(2) to (4), a utilization status of the plurality of frequency bands ismeasured during at least a part of the null periods, a frequency band tobe used, among the plurality of frequency bands, are determined on thebasis of the measurement result, and information indicating theplurality of frequency bands to be used is signaled to the terminalapparatus.

(7) In accordance with the base station apparatus according to thepresent invention, in the base station apparatus described in any one of(2) to (4), a frequency band that is not capable of being used as thededicated frequency band by the communication system is included in thesecond frequency band.

(8) A terminal apparatus according to the present invention is aterminal apparatus which is included in a communication system thatapplies a communication scheme applied to a first frequency band capableof being used as a dedicated frequency band to a second frequency banddifferent from the first frequency band and is capable of communicatingwith a base station apparatus by using the second frequency band and thesecond frequency band. The terminal apparatus: receives a frame numberof a frame of a first signal transmitted using the first frequency bandand a frame number of a frame of a second signal transmitted using thesecond frequency band from the base station apparatus; and performsmonitoring of control signals which are included in the first signal andthe second signal and are based on the communication scheme, on thebasis of the reception.

(9) In accordance with the terminal apparatus according to the presentinvention, in the terminal apparatus described in (8), a plurality offrequency bands is included in the second frequency band, and monitoringof a control signal based on the communication scheme is performed in atleast one frequency band of the plurality of frequency bands.

(10) In accordance with the terminal apparatus according to the presentinvention, in the terminal apparatus described in (9), informationindicating the second frequency band to which the first communicationscheme is applied is signaled from the base station apparatus, and themonitoring in the frequency band which is not capable of being used asthe dedicated frequency band is started on the basis of the signaling.

(11) In accordance with the terminal apparatus according to the presentinvention, in the terminal apparatus described in any one of (8) to(10), a frequency band that is not capable of being used as thededicated frequency band by the communication system is included in thesecond frequency band.

(12) A communication method according to the present invention is acommunication method used in a base station apparatus which is includedin a communication system that applies a communication scheme applied toa first frequency band capable of being used as a dedicated frequencyband to a second frequency band different from the first frequency bandand is capable of communicating with a terminal apparatus by using thesecond frequency band and the second frequency band. The communicationmethod includes: a step of synchronizing a frame number of a frame of afirst signal transmitted using the first frequency band with a framenumber of a frame of a second signal irrespective of whether or not thesecond signal transmitted using the second frequency band istransmitted.

(13) A communication method according to the present invention is acommunication method used in a terminal apparatus which is included in acommunication system that applies a communication scheme applied to afirst frequency band capable of being used as a dedicated frequency bandto a second frequency band different from the first frequency band andis capable of communicating with a base station apparatus by using thesecond frequency band and the second frequency band. The communicationmethod includes: a step of receiving a frame number of a frame of afirst signal transmitted using the first frequency band and a framenumber of a frame of a second signal transmitted using the secondfrequency band; and a step of performing monitoring of control signalswhich are included in the first signal and the second signal and arebased on the communication scheme, on the basis of the frame numbers.

Advantageous Effects of Invention

According to the present invention, a CA technology using an unlicensedband is realized in addition to a licensed band while minimizinginterference from an existing system. As a result, it is possible toimprove the throughput of a communication system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example of a communication systemaccording to the present invention.

FIG. 2 is a schematic block diagram illustrating a structure example ofa base station apparatus according to the present invention.

FIG. 3 is a schematic block diagram illustrating a structure example ofa terminal apparatus according to the present invention.

FIG. 4A is a diagram illustrating an example of a frame structure of asignal according to the present invention.

FIG. 4B is a diagram illustrating an example of the frame structure ofthe signal according to the present invention.

FIG. 4C is a diagram illustrating an example of the frame structure ofthe signal according to the present invention.

FIG. 4D is a diagram illustrating an example of the frame structure ofthe signal according to the present invention.

FIG. 5 is a schematic block diagram illustrating a structure example ofthe base station apparatus according to the present invention.

FIG. 6 is a diagram illustrating an example of the frame structure ofthe signal according to the present invention.

DESCRIPTION OF EMBODIMENTS

[First Embodiment]

A communication system according to the present embodiment includes abase station apparatus (transmission apparatus, cell, transmissionpoint, transmit antenna group, transmit antenna port group, componentcarrier, or evolved Node B (eNB)), a terminal apparatus (terminal,mobile terminal, reception point, reception terminal, receptionapparatus, receive antenna group, receive antenna port group, or userequipment (UE)).

FIG. 1 is a schematic diagram illustrating an example of a downlink of acellular system according to a first embodiment of the presentinvention. In the cellular system of FIG. 1, a base station apparatus(eNB) 1 of a wide coverage (cell radius is large) is present, and aterminal apparatus UE1 and a terminal apparatus UE2 which are coupledwith the base station apparatus 1 are present. It is assumed that astation (STA) 4 and a STA 5 which perform the existing 802.11communication are also present in the coverage range of the base stationapparatus 1, and it is assumed that the STA 4 and the STA 5 are likelyto perform communication on the basis of IEEE 802.11 system(hereinafter, simply referred to as 802.11 system) in unlicensed band.Here, the unlicensed band refers to a frequency band in which a radiocommunication operator can provide services without gaining permissionfor use by a country or a locality. That is, the unlicensed band is afrequency band in which a specific radio communication operator is notable to exclusively use. Downlink transmission will be mainly describedbelow, but a method according to the present embodiment may also beapplied to transmission (uplink) from each terminal apparatus to thebase station apparatus 1.

It is assumed that the terminal apparatus UE1 and the terminal apparatusUE2 are coupled with one of the component carriers for communicatingwith the base station apparatus 1, as a primary cell (Pcell) and afrequency band to be used is a licensed band. Here, the licensed bandrefers to a frequency band permitted for use by a country or a localityin which a radio communication operator provides services. That is, thelicensed band is a frequency band in which a specific radiocommunication operator can exclusively use.

The base station apparatus 1 according to the present embodimentperforms data communication with the terminal apparatus UE1 and theterminal apparatus UE2 through the CA using a part of the unlicensedband as a secondary cell (Scell). Thus, the terminal apparatus UE1 andthe terminal apparatus UE2 may perform monitoring of a physical downlinkcontrol channel (PDCCH) or an enhanced physical downlink control channel(EPDCCH) through which the base station apparatus 1 transmits controlinformation of downlink data transmission in the unlicensed band inaddition to the licensed band. The monitoring of the PDCCH includes asynchronization process and a blind decoding process for a search spacein order to decode downlink control information (DCI) which isinformation related to downlink control.

FIG. 2 is a block diagram illustrating a structure example of the basestation apparatus 1 according to the first embodiment of the presentinvention. As illustrated in FIG. 2, the base station apparatus 1includes a higher layer unit 101, a control unit 102, a transmissionunit 103, a reception unit 104, and an antenna 105.

The higher layer unit 101 performs processes of a medium access control(MAC) layer, a packet data convergence protocol (PDCP) layer, a radiolink control (RLC) layer and a radio resource control (RRC) layer. Thehigher layer unit 101 generates information for controlling thetransmission unit 103 and the reception unit 104, and outputs thegenerated information to the control unit 102. The higher layer unit 101may generate information for signaling a frame structure of a signalconfigured by a frame control unit 1031, to be described below, to eachterminal apparatus.

The transmission unit 103 includes the frame control unit 1031, aphysical channel signal generation unit 1032, and a wirelesstransmission unit 1034. The frame control unit 1031 determines a framestructure of a signal generated by the physical channel signalgeneration unit 1032 on the basis of an instruction from the controlunit 102. The operation details of the frame control unit 1031 will bedescribed below.

The physical channel signal generation unit 1032 generates a basebandsignal transmitted to the terminal apparatus UE1 and the terminalapparatus UE2 by the base station apparatus 1 in the Pcell and the Scellon the basis of the frame structure determined by the frame control unit1031. The signal generated by the physical channel signal generationunit 1031 includes signals transmitted through the PDCCHs of the Pcelland the Scell and a physical downlink shared channel (PDSCH) throughwhich downlink data is transmitted. Since the number of terminalapparatuses is 2 in FIG. 1, the example in which the baseband signalstransmitted to the terminal apparatus UE1 and the terminal apparatus UE2are generated is illustrated, but the present embodiment is not limitedthereto.

The wireless transmission unit 1034 performs a process of converting thebaseband signal generated by the physical channel signal generation unit1032 into a signal of a radio frequency (RF) band. The process performedby the wireless transmission unit 1034 includes digital-to-analogconversion, filtering, and frequency conversion for converting thebaseband into the RF band.

The antenna 105 transmits the signal generated by the transmission unit103 to the terminal apparatus UE1 and the terminal apparatus UE2.

The base station apparatus 1 has a function of receiving signalstransmitted from the terminal apparatus UE1 and the terminal apparatusUE2. The antenna 105 receives the signals transmitted from the terminalapparatus UE1 and the terminal apparatus UE2, and outputs the receivedsignal to the reception unit 104.

The reception unit 104 includes a physical channel signal demodulationunit 1041, and a wireless reception unit 1042. The wireless receptionunit 1042 converts a signal of the RF band input from the antenna 105into the signal of the baseband. The process performed by the wirelessreception unit 1042 includes frequency conversion for converting the RFband into the baseband, filtering, and analog-to-digital conversion. Theprocess performed by the reception unit 104 may have a function (forexample, carrier sense or listen before talk (LBT)) of measuring anambient interference and reserving the radio resource (including a timeresource, a frequency resource, and a spatial resource).

The physical channel signal demodulation unit 1041 demodulates thesignal of the baseband output by the wireless reception unit 1042. Thesignal demodulated by the physical channel signal demodulation unit 1041includes signals transmitted through a physical uplink control channel(PUCCH) through which the terminal apparatus UE1 and the terminalapparatus UE2 transmit control information of uplink data transmissionand a physical uplink shared channel (PUSCH) through which the terminalapparatuses transmit uplink data. The physical channel signaldemodulation unit 1041 may demodulate the uplink data transmittedthrough the PUSCH on the basis of control information which istransmitted through the PDCCH and is related to the uplink. The physicalchannel signal demodulation unit 1041 may have a carrier sense function.

FIG. 3 is a block diagram illustrating a structure example of theterminal apparatus UE1 and the terminal apparatus UE2 according to thepresent embodiment. As illustrated in FIG. 3, the terminal apparatus UE1and the terminal apparatus UE2 include a higher layer unit 201, acontrol unit 202, a transmission unit 203, a reception unit 204, and anantenna 205.

The higher layer unit 201 performs the processes of the MAC layer, thePDCP layer, the RLC layer, and the RRC layer. The higher layer unit 201generates information for controlling the transmission unit 203 and thereception unit 204, and outputs the generated information to the controlunit 202.

The antenna 205 receives the signal transmitted from the base stationapparatus 1, and outputs the received signal to the reception unit 204.It is assumed in the following description that the number of antennas205 included in the terminal apparatus UE1 and the terminal apparatusUE2 is one in the transmission and reception, but the terminal apparatusUE1 and the terminal apparatus UE2 may use a plurality of antennas inthe transmission and reception. The terminal apparatus UE1 and theterminal apparatus UE2 may include an antenna used in the transmissionand reception for every frequency band. The same is true of the antenna204 included in the base station apparatus 1.

The reception unit 104 includes a physical channel signal demodulationunit 2041, a PDCCH monitoring unit 2042, and a wireless reception unit2043. The wireless reception unit 2043 converts the signal of the RFband input from the antenna 205 into the signal of the baseband. Theprocess performed by the wireless reception unit 2043 includes frequencyconversion for converting the RF band into the baseband, filtering, andanalog-to-digital conversion.

The PDCCH monitoring unit 2042 performs monitoring of the PDCCH or theEPDCCH on the signal of the baseband output from the wireless receptionunit 2043, and acquires the control information transmitted from thebase station apparatus 1 through the PDCCH or the EPDCCH. The PDCCHmonitoring unit 2042 may perform the synchronization process on thebasis of a signal (for example, primary synchronization signal (PSS) orsecondary synchronization signal (SSS)) of a synchronization channeltransmitted from the base station apparatus 1.

The physical channel signal demodulation unit 2041 demodulates thesignal of the baseband output from the wireless reception unit 2043 onthe basis of the control information acquired by the PDCCH monitoringunit 2042. The signal demodulated by the physical channel signaldemodulation unit 2041 includes a signal transmitted from the basestation apparatus 1 through the PDSCH. The physical channel signaldemodulation unit 2041 may demodulate the downlink data transmittedthrough the PDSCH on the basis of the DCI transmitted through the PDCCH.

The terminal apparatus UE1 and the terminal apparatus UE2 have afunction of transmitting a signal. The antenna 205 transmits the signalof the RF band generated by the transmission unit 203 to the basestation apparatus 1.

The transmission unit 203 includes a physical channel signal generationunit 2031, and a wireless transmission unit 2032. The physical channelsignal generation unit 2031 generates the signal of the basebandtransmitted to the base station apparatus 1 from the terminal apparatusUE1 and the terminal apparatus UE2. The signal generated by the physicalchannel signal generation unit 2031 includes signals transmitted fromthe terminal apparatus UE1 and the terminal apparatus UE2 through thePUCCH and the PUSCH.

The wireless transmission unit 2032 converts the signal of the basebandgenerated by the physical channel signal generation unit 2031 into thesignal of the RF band. The process performed by the wirelesstransmission unit 2032 includes digital-to-analog conversion, filtering,and frequency conversion for converting the baseband into the RF band.

In the present embodiment, it is considered that the base stationapparatus 1 performs the carrier aggregation (CA) on the terminalapparatus UE1 and the terminal apparatus UE2 using a part of theunlicensed band as the secondary cell (Scell). However, if thecommunication system continuously occupies the unlicensed band on thebasis of the LTE system, another apparatus that performs communicationby another existing communication system represented by the 802.11system may not perform the communication in the unlicensed band. Thebase station apparatus 1 is not able to perform the carrier sense inthis frequency band while performing communication using a part of theunlicensed band as the Scell.

Thus, the frame control unit 1031 of the base station apparatus 1according to the present embodiment controls such that a signaltransmitted in the Scell and a signal transmitted from the base stationapparatus 1 in the Pcell based on the LTE system have different framestructures.

FIG. 4A is a diagram illustrating an example of a frame structureconfigured by the frame control unit 1031 according to the presentembodiment. A frame (LTE frame) based on the LTE system includes 10subframes (LTE subframes) each having a length of 1 millisecond (ms),and has a length of 10 ms. In the present embodiment, the signaltransmitted from the base station apparatus 1 in the Pcell of thelicensed band has the frame structure of the LTE system.

Meanwhile, in the present embodiment, in the frame structure of thesignal transmitted from the base station apparatus 1 in the Scell of theunlicensed band, a frame length is 10 ms which is the same as that ofthe LTE frame, and the number of subframes constituting the frame isless than 10. That is, the frame control unit 1031 assigns a no-signalperiod (period expressed as null in FIG. 4) during which there is nosignal to the frame of the signal transmitted from the base stationapparatus 1 in the Scell of the unlicensed band. The number of subframesconstituting the frame is not a natural number, and may be a numberexpressed by a radix point, such as “8.5 frame”. The frame control unit1031 controls such that a total period of the period during which theLTE subframes are allocated and the no-signal period is the same as theframe length of the LTE frames transmitted from the base stationapparatus 1 in the Pcell of the licensed band. That is, the frame lengthof the signal of the Scell configured by the frame control unit 1031 isconstantly a predetermined length (for example, 10 ms), and the framelength of the signal is not present in the number of LTE subframesincluded in the frame of one signal, the length of the no-signal period,or the position to be allocated. The frame control unit 1031 configuressuch a frame structure, and thus, each apparatus including the basestation apparatus 1, which is included in the communication system, canperform the carrier sense during the null period. For example, the STA 4or the STA 5 can start the communication on the basis of an accessscheme called carrier sense multiple access with collision avoidance(CSMA/CA).

As the method of causing the base station apparatus 1 to assign the nullperiod to the frame of the signal transmitted in the Scell, the framecontrol unit 1031 may control such that the frame of the signaltransmitted in the Scell includes a plurality of signal frames and nullframes. Here, it is assumed that the null frame is the frame that doesnot include the signal. It is assumed that the signal frame is the frame(for example, LTE subframe) that includes the signal. The null framelength is not limited to any length, and, for example, the frame controlunit 1031 may set the null frame length and the LTE subframe length tobe the same. The frame control unit 1031 configures the frame of thesignal transmitted in the Scell such that a total period of theplurality of LTE subframes and the null frames is the same as the LTEframe length transmitted from the base station apparatus 1 in the Pcellof the licensed band. The null period is not necessarily configured forthe last LTE frame, and may be configured for the leading LTE frame.

The no-signal period in the present embodiment includes a case whereeach apparatus transmits the signal with a transmit power or a channelstructure such that the signal transmitted from each apparatus isreceived with the following received power which is equal to or lessthan a prescribed power (for example, carrier sense level) by anapparatus other than this base station apparatus in the radio resourcein addition to a case where each apparatus completely stops transmittingthe signal. For example, the base station apparatus 1 may control suchthat only the signal (for example, PSS or SSS) of the synchronizationchannel is transmitted in the no-signal period. The base stationapparatus 1 may control such that only the system information (forexample, a broadcast information transmitted from the base stationapparatus 1 in physical broadcast channel (PBCH) or Beacon frame used inthe IEEE 802.11 system) of this base station apparatus is transmitted inthe no-signal period.

The base station apparatus 1 may control such that the signal of thesynchronization channel such as the PSS or the SSS is not transmitted inthe Scell of the unlicensed band and the signal of the synchronizationchannel such as the PSS or the SSS is transmitted in the Pcell of thelicensed band in the no-signal period.

Although it has been described in FIG. 4A that a null period of 1 ms isprovided for every four subframes, that is, every 4 ms, the length ofthe null period or the number of subframes until reaching the nullperiod is not limited to the method illustrated in FIG. 4A. However, thelength of the null period is appropriately an integral multiple of thesubframe length, but is not limited thereto. The frame control unit 1031may periodically assign the null period to the frame of the signal ofthe Scell, or may adaptively assign the null period on the basis of thetraffic amount of the communication system.

The higher layer unit 101 may add the frame structure of the signalwhich is configured by the frame control unit 1031 and is transmitted inthe Scell of the unlicensed band to the higher layer signal such as aradio resource control (RRC) signal which is addressed to each terminalapparatus. The higher layer unit 101 may be operated such thatinformation indicating the plurality of frame structures that is likelyto be configured by the frame control unit 1031 is previously signaledto each terminal apparatus, or the higher layer unit 101 may be operatedsuch that information indicating priorities configured for the pluralityof subframe structures by the frame control unit 1031 is previouslysignaled to each terminal apparatus. The base station apparatus 1 mayadd information indicating the frame structure among the plurality offrame structures signaled to each terminal apparatus from the higherlayer unit 101, which is used by the frame control unit 1031 in realityto another control information (for example, control informationtransmitted in the PDCCH and the EPDCCH of the Pcell and the Scell). Thecontrol information may be information indicating the position of thenull period assigned to the frame of the signal transmitted by the framecontrol unit 1031 in the Scell of the unlicensed band, or may beinformation indicating the position of the LTE subframe transmitted inthis frame.

The base station apparatus 1 may not explicitly notify each terminalapparatus of the frame structure configured by the frame control unit1031. For example, the terminal apparatus UE1 and the terminal apparatusUE2 may recognize information (for example, cell ID) indicating the basestation apparatus 1 to which this base station apparatus is coupled fromthe another signal (for example, the signal transmitted in the PSS orthe SSS) transmitted from the base station apparatus 1. In this case,the frame structure configured by the frame control unit 1031 ispreviously associated with the cell ID, and thus, the terminal apparatusUE1 and the terminal apparatus UE2 may recognize the frame structureconfigured by the frame control unit 1031. The base station apparatus 1may previously signal a table indicating the relationship between theframe structure configured by the frame control unit 1031 and the cellID to each terminal apparatus.

The wireless reception unit 1042 or the physical channel signaldemodulation unit 1041 may perform the carrier sense during the nullperiod. The frame control unit 1031 may change the frame structure onthe basis of the result of the carrier sense. For example, in a casewhere the unlicensed band is not able to be reserved through the carriersense, the frame control unit 1031 may set the period of the LTEsubframe subsequent to the null period as the null period.

In a case where the frame control unit 1031 adds a null to the frame ofthe signal of the Scell on the basis of the result of the carrier sense,the base station apparatus 1 may signal the frame structure configuredby the frame control unit 1031 to each terminal apparatus again by thesignal of the higher layer or the control information transmittedthrough the PDCCH. In a case where the base station apparatus 1 signalsthe frame structure configured by the frame control unit 1031 by thecontrol information transmitted through the PDCCH, the base stationapparatus may signal only differential information from the framestructure previously notified to each terminal apparatus through thesignaling of the higher layer.

The frame control unit 1031 may apply almost blank subframe (ABS)standardized by LTE in order to assign the null period to the frame ofthe signal transmitted in the Scell. The ABS is a technology for causingthe base station apparatus (or the terminal apparatus) to reduce a partof the transmit power of the physical channel (for example, PDSCH orPDCCH) in a part of the subframes or to stop the transmission in orderto mainly suppress the interference between the neighboring cells. Theframe control unit 1031 may create the null period by stopping thetransmission of a part of the subframes of the frame of the signaltransmitted in the Sell or reducing the transmit power through the ABS.The frame control unit 1031 may periodically dispose the null period byperiodically applying the ABS to the frame of the signal transmitted inthe Scell (for example, every 4 ms).

In the present embodiment, the null period configured by the framecontrol unit 1031 is not necessarily use for suppressing theinterference between the neighboring cells. Thus, in a case where thecommunication system according to the present embodiment includes aplurality of base station apparatus and each base station apparatusapplies the null period to the frame of the signal transmitted in theScell of the unlicensed band in the ABS, it is not necessary to staggera timing when the null period is assign to the frame of the signalbetween neighboring base station apparatus. In order to suppressinterfering and being interfered from another system represented by theIEEE 802.11 system, the timing when the null period is assigned to theframe of the signal is appropriately matched between the neighboringbase station apparatus.

Meanwhile, the terminal apparatus UE1 and the terminal apparatus UE2perform the demodulation process on the signal transmitted in theunlicensed band on the basis of the information indicating the framestructure of the signal transmitted in the Scell of the unlicensed bandsignaled by the base station apparatus 1. In this case, the PDCCHmonitoring unit 2042 may stop monitoring the control information duringthe null period assigned to the frame of the signal transmitted in theScell. In a case where the base station apparatus 1 transmits only thesynchronization channel during the null period, the PDCCH monitoringunit 2042 may perform only the synchronization process during the nullperiod.

The frequency band in which the base station apparatus 1 according tothe present embodiment performs the CA is not limited to the licensedband or the unlicensed band described above. The frequency band as atarget of the present embodiment includes a frequency band (for example,a frequency band which is allocated for television broadcasting but isnot used by the locality) called a white band that is not used inreality in order to prevent the crosstalk between frequencies eventhough the permission for use of a specific service is gained by acountry or a locality, or a shared frequency band which is exclusivelyallocated to a specific operator but is expected to be shared between aplurality of operators in the future. For example, a case where the basestation apparatus 1 configures the Pcell for the licensed band andconfigures the Scell for a part of the white band is also included inthe present embodiment. The frame control unit 1031 may change thestructure of the frame of the signal of the Scell depending on thefrequency band in which the base station apparatus 1 configures theScell.

In accordance with the method according to the present embodiment, thebase station apparatus 1 can assign the null period to the frame of thesignal transmitted in the Scell of the unlicensed band. Each apparatusincluded in the communication system can also perform communication onthe basis of a communication method (for example, CSMA/CA) of anothersystem during the null period. Accordingly, since a specific apparatusdoes not occupy the unlicensed band during a long period, the basestation apparatus 1 can improve the throughput of the communicationsystem through the CA using the unlicensed band while minimizing theinfluence on another system.

[Second Embodiment]

Similarly to the first embodiment, it is also assumed in the presentembodiment that the terminal apparatus UE1 and the terminal apparatusUE2 are coupled with the base station apparatus 1 as the Pcell and thefrequency band to be used is the licensed band.

FIG. 5 is a block diagram illustrating a structure example of the basestation apparatus 1 according to the present embodiment. The basestation apparatus 1 according to the present embodiment has a differencefrom the base station apparatus 1 according to the first embodiment inthat the transmission unit 103 further includes a control signalgeneration unit 1035 and a multiplexing unit 1036. It is assumed thatthe outline of the communication system according to the presentembodiment and the structures of the terminal apparatus UE1 and theterminal apparatus UE2 are the same as those of the first embodiment.

The control signal generation unit 1035 generates a signal includingcontrol information (for example, control information transmittedthrough the PDCCH of the Pcell and the Scell) transmitted to theterminal apparatus UE1 and the terminal apparatus UE2 from the basestation apparatus 1. The multiplexing unit 1036 multiplexes the signalgenerated by the physical channel signal generation unit 1031 and thesignal generated by the control signal generation unit 1035.

Similarly to the first embodiment, in the present embodiment, the basestation apparatus 1 performs the CA using the unlicensed band as theScell. The base station apparatus 1 transmits a resource reservingsignal for previously reserving the unlicensed band in at least apartial range of the coverage range of this base station apparatusduring the null period assigned to the frame of the signal transmittedfrom the frame control unit 1031 in the Scell.

FIG. 4B is a diagram illustrating an example of the frame structureconfigured by the frame control unit 1031 according to the presentembodiment. The signal transmitted from the base station apparatus 1 inthe Pcell of the licensed band has the same structure as that of FIG.4A. Meanwhile, similarly to FIG. 4A, a null period of a predeterminedperiod is assigned in the frame structure of the signal transmitted inthe Scell of the unlicensed band configured by the frame control unit1031, but the frame control unit 1031 assigns a period (radio resource)during which the resource reserving signal is transmitted to theunlicensed band to the null period. By controlling the period in thismanner, the base station apparatus 1 can reserve the unlicensed bandduring the period later than the null period.

The resource reserving signal transmitted from the base stationapparatus 1 according to the present embodiment is not particularlylimited. For example, the base station apparatus can generate theresource reserving signal and transmit the generated resource reservingsignal on the basis of an interference protection technology used in theIEEE 802.11 system.

In the CSMA/CA adopted by the IEEE 802.11 system, autonomousmulti-access is realized by performing communication in a case whereeach terminal apparatus performs the carrier sense and interference isnot measured. However, since there are limitations in a distance(referred to as a carrier sense area) at which the carrier sense can beperformed, two terminal apparatuses that are away from their carriersense areas simultaneously transmit the signals, so that interferencemay be caused in the other terminal apparatus in some cases. Thus,several interference protection technologies are adopted by the IEEE802.11 system.

In Request-to-Send/Clear-to-Send (RTS/CTS), a terminal apparatus thatdesires to transmit the signal transmits the RTS to a terminal apparatusas a transmission destination. If the terminal apparatus as thedestination of the RTS performs the carrier sense after receiving theRTS and the interference is not measured (observed), this terminalapparatus transmits the CTS to the terminal apparatus that transmits theRTS. In this case, a terminal apparatus other than the terminalapparatus as the destination of the RTS that receives the RTS and aterminal apparatus other than the terminal apparatus as the destinationof the CTS that receives the CTS stop transmitting packets during apreviously configured period of the network allocation vector (NAV).Accordingly, in the carrier sense of at least the terminal apparatus asthe destination of the RTS and the terminal apparatus as the destinationof the CTS, interference does not occur.

Meanwhile, CTS-to-self is a function of causing the terminal apparatusthat desires to transmit the signal to transmit the CTS to this terminalapparatus itself. As described above, since the terminal apparatus otherthan the terminal apparatus as the destination of the CTS that receivesthe CTS stops transmitting the packet between the NAVs, the terminalapparatus transmits the CTS-to-self, so that the interference from atleast an area where the CTS-to-self reaches does not occur.

Thus, the control signal generation unit 1035 according to the presentembodiment generates the CTS-to-self as the resource reserving signal.The multiplexing unit 1036 multiplexes the resource reserving signalgenerated by the control signal generation unit 1035 and the signalgenerated by the physical channel signal generation unit 1032 such thatthese signals are allocated to the radio resources in which the resourcereserving signal configured by the frame control unit 1031 istransmitted. The control signal generation unit 1035 may transmit theRTS or the CTS as the resource reserving signal instead of theCTS-to-self. In the RTS or the CTS (including the CTS-to-self), since avalue of the NAV can be notified to the apparatus capable of receivingthe RTS (or the CTS), the control signal generation unit 1035 candescribe the value of the NAV as the RTS (or the CTS) on the basis ofthe number of subframes transmitted after the null period in a casewhere the RTS or the CTS is generated as the resource reserving signal.

If the timing when the resource reserving signal configured by the framecontrol unit 1031 is transmitted is not limited as long as this timingis within the null period, and is preferably configured such that atleast the base station apparatus 1 can perform the carrier sense duringthe null period. In a case where the control signal generation unit 1035generates the CTS-to-self as the resource reserving signal, it isassumed that the next signal is transmitted after a short interframespace (SIFS) period after the reception of the CTS is completed in theIEEE 802.11 system. This indicates that the frame control information1031 can also control a transmission timing of the LTE subframetransmitted after the resource reserving signal is transmitted bycontrolling a transmission timing of the resource reserving signal. Forexample, the frame control information 1031 can also control thetransmission timing of the resource reserving signal so as to improvesynchronization accuracy between the frame of the signal transmitted inthe Pcell and the frame of the signal transmitted in the Scell.

FIG. 6 is a schematic diagram illustrating an example of a method oftransmitting the resource reserving signal during the null periodaccording to the present embodiment. The wireless reception unit 1042 orthe physical channel signal demodulation unit 1941 of the base stationapparatus 1 starts the carrier sense in the unlicensed bandsimultaneously with the starting of the null period of the frame duringwhich the transmission in the Scell of the unlicensed band is performed.In a case where it is determined that the unlicensed band can bereserved, the frame control unit 1031 determines the transmission timingof the resource reserving signal such that a resource reserving signaltransmission period and a period after a SIFS period become atransmission starting timing of the LTE subframe transmitted from thebase station apparatus 1 in the Pcell of the licensed band. In a casewhere the control signal generation unit 1035 generates an appropriatesignal (may be a signal such as impulse signal) as the resourcereserving signal, the frame control unit 1031 may determine thetransmission timing of the resource reserving signal such that theresource reserving signal transmission and a period after a distributedcoordination function IFS (DIFS) period become the a transmissionstarting time of the LTE subframe transmitted from the base stationapparatus 1 in the Pcell of the licensed band. By controlling the periodin this manner, the base station apparatus 1 can more efficientlyreserve the radio resource, and can synchronize the LTE frametransmitted in the Pcell of the licensed band and the LTE frametransmitted in the Scell of the unlicensed band with high accuracy.

The frame control unit 1031 may perform the transmission timing of theresource reserving signal illustrated in FIG. 6 during all the nullperiods. The frame control unit 1031 may control such that the resourcereserving signal is transmitted during the null period and also suchthat the leading LTE frames transmitted in the Pcell and the Scell aresynchronized, or the frame control unit 1031 may adaptively determinethe null period during which the resource reserving signal istransmitted. For example, in a case where the frame control unit 1031requires the synchronization of the LTE frames transmitted in the Pcelland the Scell (for example, a case where the base station apparatus 1transmits the control information in order to demodulate the controlinformation of the PDSCH of the Scell by using the PDCCH of the Pcell),the frame control unit may control such that the resource reservingsignal is transmitted during the null period.

In accordance with the method according to the present embodiment, thebase station apparatus 1 can transmit the resource reserving signal inthe unlicensed band during the null period assigned to the frame of thesignal transmitted in the Scell of the unlicensed band. Accordingly,since the unlicensed band can be more efficiently reserved, the basestation apparatus 1 can improve the throughput of the communicationsystem through CA using the unlicensed band.

[Third Embodiment]

Similarly to the first embodiment, it is also assumed in the presentembodiment that the terminal apparatus UE1 and the terminal apparatusUE2 are coupled with the base station apparatus 1 as the Pcell and thefrequency band to be used is the licensed band. It is assumed that theoutline of the wireless communication system, the structure of the basestation apparatus 1, and the structures of the terminal apparatus UE1and the terminal apparatus UE2 according to the present embodiment arethe same as those of the first embodiment.

Similarly to the first embodiment, in the present embodiment, the basestation apparatus 1 performs CA using the unlicensed band as the Scell.The null period is assigned to the frame of the signal transmitted fromthe base station apparatus 1 in the Scell. It is assumed that thewireless reception unit 1042 or the physical channel signal demodulationunit 1041 performs the carrier sense in the unlicensed band during thenull period.

In a case where the base station apparatus 1 is not able to reserve theunlicensed band as the result of the carrier sense during the nullperiod, the base station apparatus 1 does not transmit the signal in theScell of the unlicensed band after the null period. Meanwhile, the basestation apparatus 1 can continue to transmit the signal in the Pcell ofthe licensed band irrespective of the result of the carrier sense of theunlicensed band. In this case, there is a problem that the number offrames of the signal transmitted from the base station apparatus 1 inthe Pcell of the licensed band and the number of frames of the signaltransmitted in the Scell of the unlicensed band are different.

Thus, in the present embodiment, the frame control unit 1031 measuresthe number of frames of the signal irrespective of the result of thecarrier sense performed during the null period assigned to the frametransmitted from the base station apparatus 1 in the Scell of theunlicensed band.

FIG. 4C is a diagram illustrating an example of the frame structureconfigured by the frame control unit 1031 according to the presentembodiment. The signal transmitted from the base station apparatus 1 inthe Pcell of the licensed band has the same structure as that of FIG.4A. Similarly to FIG. 4A, in the frame structure of the signaltransmitted in the Scell of the unlicensed band configured by the framecontrol unit 1031, a null period of a predetermined length (1 ms) isassigned for every a predetermined period (every 4 ms). The wirelessreception unit 1042 or the physical channel signal demodulation unit1041 performs the carrier sense in the unlicensed band during each nullperiod. FIG. 4C illustrates a case where the base station apparatus 1 isnot able to reserve the unlicensed band during Period 1 and Period 2 asan example of the result of the carrier sense and another base stationapparatus (for example, STA 4 or STA 5) performs communication in theunlicensed band. It is assumed that a no-transmission period of thesignal transmitted in the Scell of the unlicensed band originallyconfigured by the frame control unit 1031 is referred to as the nullperiod and a no-transmission period occurring as the result due to theuse of the unlicensed band by another system is referred to as an idleperiod in the present embodiment.

In this case, the LTE frame is able to be transmitted during Period 1and Period 2 in the unlicensed band, and the frame control unit 1031counts up a frame number (system frame number (SFN)). In FIG. 4C, LTEframe n indicates that the SFN is n. For example, LTE frame 1 indicatesthat the SFN is 1.

In the LTE system, since one LTE frame (a periodicity of 10 ms) includes10 LTE subframes, if 10 LTE subframes are transmitted, the frame controlunit 1031 increases the SFN by 1.

However, in FIG. 4C, in the case of the signal transmitted in the Scellof the unlicensed band, since another system uses the unlicensed bandduring Period 1, only four LTE subframes are transmitted during thefirst periodicity of 10 ms. Even in this case, the frame control unit1031 counts up the SFN so as to match with the SFN of the signaltransmitted in the Pcell of the licensed band. Thus, the unlicensed bandafter the idle period can be reserved through the carrier sense of thebase station apparatus 1 during the idle period after the communicationis performed by the another system, and the SFN of the signaltransmitted in the Scell of the unlicensed band becomes 2. That is, inaccordance with the method according to the present embodiment, theframe control unit 1031 can increase the SFN assigned to the frametransmitted in the Scell of the unlicensed band at a timing when the SFNassigned to the frame transmitted in the Pcell of the licensed bandduring the period is increased irrespective of whether or not the basestation apparatus 1 transmits the signal in the Scell in reality.Accordingly, the base station apparatus 1 can set the SFN of the signaltransmitted in the Pcell to be the same as the SFN of the signaltransmitted in the Scell.

The base station apparatus 1 can reserve the unlicensed band for aperiod during which the base station apparatus 1 transmits the LTE frame2 in the Pcell of the licensed band, but the number of LTE subframescapable of being transmitted from the base station apparatus 1 in theScell of the unlicensed band does not reach 10 due to the null periodassigned by the frame control unit 1031. Even in this case, the framecontrol unit 1031 controls the SFN of the frame transmitted from thebase station apparatus 1 in the Scell of the unlicensed band during thisperiod so as to become 2.

Since the unlicensed band is used by another system over the entireperiod for a period during which the base station apparatus 1 transmitsthe LTE frame 3 in the Pcell of the licensed band, the base stationapparatus 1 is not able to transmit the signal in the Scell of theunlicensed band. Even in this case, the frame control unit 1031 controlsthe SFN of the frame on the assumption that the base station apparatus 1transmits the LTE frame of which the SFN is 3 in the Scell of theunlicensed band during this period. The frame control unit 1031 performsthe same process for a period during which the base station apparatus 1transmits the LTE frame 4 in the Pcell of the licensed band.

The frequency band in which the base station apparatus 1 according tothe present embodiment configures the Scell is not limited to theunlicensed band, and includes, for example, a frequency band called awhite space or a frequency band shared between the plurality ofoperators. Since these frequency bands have different performances, theframe control unit 1031 can change the frame structure of the signal ofthe Scell depending on the frequency band in which the Scell isconfigured. Here, the performance of the frequency band includesperformance characterized by a legal regulation such as an allowablesignal burst length in addition to physical performance represented bychannel quality. The frame control unit 1031 can change the number oftimes the LTE frame is transmitted depending on the frequency band inwhich the Scell is configured. As stated above, the base stationapparatus 1 selects the frequency band in which the Scell is configuredfrom the plurality of frequency bands including the unlicensed band, andthe frame control unit 1031 can set the SFN of the signal transmitted inthe Pcell to match with the SFN of the signal transmitted in the Scelleven in a case where the frame control unit 1031 configures the framestructure of the signal of the Scell depending on the frequency band.

In a case where the base station apparatus 1 can use the plurality offrequency bands, the base station apparatus 1 can previously determinepriority levels for applying the CS for the plurality of frequencybands. The base station apparatus 1 can previously notify each terminalapparatus of the priority levels through the signaling of the higherlayer. The base station apparatus 1 measures the utilization status ofthe plurality of frequency bands (for example, the base stationapparatus 1 can measure an interference power of the frequency band byperforming the carrier sense), and can determine the frequency bandamong the plurality of frequency bands, which is used in CA based on themeasurement result. The base station apparatus 1 can perform thesignaling (for example, signaling of the higher layer or signaling dueto the PDCCH) of information indicating the frequency band to which CAdetermined based on the measurement result is applied to each terminalapparatus.

The PDCCH monitoring unit 2042 of the terminal apparatus UE1 and theterminal apparatus UE2 can perform the monitoring of the control signalon the plurality of frequency bands. The PDCCH monitoring unit 2042 ofthe terminal apparatus UE1 and the terminal apparatus UE2 can performthe monitoring of the control signal on only the previously notifiedfrequency band through the signaling of the higher layer from the basestation apparatus 1.

In accordance with the method according to the present embodiment, thebase station apparatus 1 can constantly set the SFN of the frame of thesignal transmitted in the Pcell of the licensed band to be the same asthe SFN of the frame of the signal transmitted in the Scell of theunlicensed band irrespective of the result of reserving the resource ofthe unlicensed band. Accordingly, since the base station apparatus 1 caneasily perform the process such as cross carrier scheduling fortransmitting the control information for demodulating the signaltransmitted in the PDSCH of the Scell by using the PDCCH of the Pcell,the base station apparatus can perform CA using a part of the unlicensedband as the Scell with higher efficiency.

[Fourth Embodiment]

Similarly to the first embodiment, it is also assumed in the presentembodiment that the terminal apparatus UE1 and the terminal apparatusUE2 are coupled with the base station apparatus 1 as the Pcell and thefrequency band to be used is the licensed band. It is assumed that theoutline of the wireless communication system, the structure of the basestation apparatus 1, and the structures of the terminal apparatus UE1and the terminal apparatus UE2 according to the present embodiment arethe same as those of the second embodiment. In the wirelesscommunication system according to the present embodiment, it is assumedthat time division duplex (TDD) is used as a duplex scheme.

Similarly to the first embodiment, the base station apparatus 1 performsCA using the unlicensed band as the Scell. The base station apparatus 1according to the present embodiment allocates a part of the unlicensedband to the Scell of the communication (uplink) from the terminalapparatus to the base station apparatus.

FIG. 4D is a diagram illustrating an example of the frame structureconfigured by the frame control unit 1031 according to the presentembodiment. The frame of the signal transmitted from the base stationapparatus 1 in the Pcell of the licensed band includes a downlinksubframe (DL SF) in which a downlink signal (for example, a signaltransmitted in the PDCCH or the PDSCH) is transmitted, an uplinksubframe (UL SF) in which an uplink signal (for example, a signaltransmitted in the PUCCH or the PUSCH) is transmitted, a downlink signaland an uplink signal in one subframe, and a special subframe (SP SF)which includes a period during which a transmission timing of the uplinkis adjusted. The order or proportion of each of the SFs constituting theframe is not particularly limited, and the frame control unit 1031 mayadaptively change the frame structure depending on a channel statebetween the terminal apparatuses and a data traffic status of thecommunication system. The frame structure of the signal configured bythe frame control unit 1031 is previously notified to each terminalapparatus from the base station apparatus 1 through, for example, thesignaling of the higher layer or L1/L2 signaling.

Meanwhile, the frame control unit 1031 configures the no-signal period(null period) as the frame of the signal transmitted from the basestation apparatus 1 in the Scell of the unlicensed band in addition tothe DL SF or the UL SF. Since the base station apparatus 1, the terminalapparatus UE1, and the terminal apparatus UE2 according to the presentembodiment can perform the carrier sense in the unlicensed band duringthe null period, the unlicensed band can be efficiently reserved.Although the SP SF is not included in the signal transmitted in theScell in FIG. 4D, it is needless to say that a case where the SP SF isincluded in the signal transmitted in the Scell is also included in themethod according to the present embodiment.

All the respective apparatuses included in the communication system mayperform the carrier sense during the null period included in the frameof the signal transmitted in the Scell of the unlicensed band, but onlya specific apparatus may perform the carrier sense. For example, onlythe apparatus that transmits the signal after the null period mayperform the carrier sense. In this case, the base station apparatus 1may perform the carrier sense during the null period configured by theframe control unit 1031 before the DL SF, and the terminal apparatus UE1and the terminal apparatus UE2 may perform the carrier sense during thenull period configured by the frame control unit 1031 before the UL SF.

The base station apparatus 1 may constantly perform the carrier senseduring the null period. For example, the base station apparatus 1 mayperform the carrier sense during the null period configured by the framecontrol unit 1031 before the UL SF, and may signal notificationindicating that the terminal apparatus UE1 and the terminal apparatusUE2 are permitted to transmit the UL SF after the null period to eachterminal apparatus in a case where it is determined that the unlicensedband can be reserved. Similarly to the second embodiment, the basestation apparatus 1 may transmit the resource reserving signal (forexample, CTS-to-self) for reserving the unlicensed band after thecarrier sense. The above-described operations may be performed by theterminal apparatus. That is, the terminal apparatus UE1 may perform thecarrier sense in the unlicensed band during the null period, and cansignal the permission for use of the unlicensed band after the nullperiod to the respective apparatuses (here, the base station apparatus 1and the terminal apparatus UE2) in a case where it is determined thatthe unlicensed band can be reserved.

In a case where the base station apparatus 1, the terminal apparatusUE1, and the terminal apparatus UE2 are not able to reserve theunlicensed band as the result of the carrier sense on the unlicensedband during the null period, the apparatuses do not transmit the DL SFor the UL SF configured by the frame control unit 1031 after the nullperiod. In this case, similarly to the third embodiment, the respectiveapparatuses may synchronize the SFN of the frame of the signaltransmitted in the Scell of the unlicensed band with the SFN of theframe of the signal transmitted in the Pcell of the licensed bandirrespective of the transmission state of the DL SF or the UL SF. Theterminal apparatus UE1 and the terminal apparatus UE2 may perform thecarrier sense, and only the terminal apparatus UE1 may transmit the ULSF in a case where only the terminal apparatus UE1 can reserve theunlicensed band.

In accordance with the method according to the present embodiment, evenin the wireless communication system that uses the TDD as the duplexscheme, the base station apparatus 1, the terminal apparatus UE1, andthe terminal apparatus UE2 can efficiently reserve the unlicensed band.The carrier sense in the unlicensed band may be performed by only thebase station apparatus 1, and thus, the complexity of the terminalapparatus 1 and the terminal apparatus UE2 can be reduced.

[Common to all Embodiments]

The programs operated in the base station apparatus and the terminalapparatuses according to the present invention may be programs (programscausing a computer to function) for controlling a CPU such that thefunctions of the above-described embodiments according to the presentinvention are realized. The information items treated by theseapparatuses are temporally accumulated in a RAM during the processing,are stored in various ROMs or HDDs, are read by the CPU if necessary,and are modified and rewritten. Here, as a recording medium that storesthe programs, any one of a semiconductor medium (for example, ROM ornon-volatile memory card), an optical recording medium (for example,DVD, MO, MD, CD, and BD), a magnetic recording medium (for example,magnetic tape and flexible disk) may be used. Not only the functions ofthe above-described embodiments may be realized by executing the loadedprogram, but also the functions of the present invention may be realizedby processing the loaded program in cooperation with an operating systemor another application program based on an instruction of the program.

In a case where the program is distributed to the market, the programmay be distributed while being stored in a portable recording medium,and may be transmitted to a server computer coupled via a network suchas the Internet. In this case, a storage device of the server computermay also be included in the present invention. Some or all of theterminal apparatuses and the base station apparatus of theabove-described embodiments may be typically realized as large scaleintegration (LSI) which is integrated circuit. The functional blocks ofthe terminal apparatuses and the base station apparatus may beseparately realized as chips, or some or all thereof may be integratedand realized as chips. In a case where the respective functional blocksare realized as the integrated circuits, an integrated circuit controlunit for controlling these circuits is provided.

The method of realizing the functional blocks as the integrated circuitis not limited to the LSI, and the functional blocks may be realized asa dedicated circuit or a general-purpose processor. Alternatively, someof the dedicated circuits are realized as general-purpose processors,and some of the respective processes or functions are realized using thegeneral-purpose processors and are realized by both a dedicated circuitunit and a software process. In a case where a technology of realizingthe apparatuses or functional blocks as the integrated circuit hasappeared instead of the LSI due to the advance of semiconductortechnology, it is possible to use an integrated circuit produced usingthis technology.

The present invention is not limited to the above-described embodiments.The terminal apparatus according to the present invention is not limitedto the application to a mobile station apparatus, and may be applied tostationary or non-movable electronic devices which are installed indoorsor outdoors, such as AV devices, kitchen devices, cleaning and washingmachines, air conditioners, office devices, vending machines, and otherhome appliances.

The embodiments of the present invention have been described withreference to the drawings. However, the detailed structure is notlimited to the above-described embodiments, and changes in the designwithin the gist of the invention may also be included in the claims.

Industrial Applicability

The present invention is suitable for a base station apparatus, aterminal apparatus, and a communication method.

The present international application claims priority based on JapanesePatent Application No. 2014-122302 filed on Jun. 13, 2014, and theentire content of Japanese Patent Application No. 2014-122302 isincorporated by reference in the present international application.

Reference Signs List

1 Base station apparatus

UE1, UE2 Terminal apparatus

4,5 STA

101, 201 Higher layer unit

102, 202 Control unit

103, 203 Transmission unit

104, 204 Reception unit

105, 205 Antenna

1031 Frame control unit

1032, 2031 Physical channel signal generation unit

1034, 2032 Wireless transmission unit

1035 Control signal generation unit

1036 Multiplexing unit

1041, 2041 Physical channel signal demodulation unit

1042, 2043 Wireless reception unit

2042 PDCCH monitoring unit

The invention claimed is:
 1. A base station apparatus which communicateswith a terminal apparatus, the base station apparatus comprising: atransmission unit that transmits a downlink signal to the terminalapparatus by performing carrier aggregation using one primary cell andone or a plurality of secondary cells, wherein the primary cell is acomponent carrier of a licensed band, and at least one secondary cell isa component carrier of an unlicensed band, a frame of the componentcarrier of the licensed band includes a transmission period of thedownlink signal, a frame of the component carrier of the unlicensed bandincludes a transmission period of the downlink signal and a null periodduring which the base station apparatus does not transmit a signal, thecomponent carrier of the unlicensed band includes a plurality of framestructures, and priorities are configured for the plurality of framestructures.
 2. The base station apparatus according to claim 1, whereinthe transmission period during which the downlink signal of theunlicensed band is transmitted includes a plurality of continuoussubframes, and the number of the plurality of continuous subframes inthe unlicensed band is equal to or less than the number of a pluralityof subframes in the licensed band.
 3. The base station apparatusaccording to claim 1, wherein the downlink signal includes downlinkcontrol information, and the downlink control information includesinformation indicating a position of the null period.
 4. The basestation apparatus according to claim 1, wherein at least one subframe ofthe plurality of subframes includes a transmission period and a nullperiod.
 5. The base station apparatus according to claims 1, furthercomprising: a reception unit that performs carrier sense during the nullperiod, wherein the transmission unit transmits the downlink signalafter carrier sense in the component carrier of the unlicensed band isperformed.
 6. A terminal apparatus that communicates with a base stationapparatus, the terminal apparatus comprising: a reception unit thatreceives a downlink signal from the base station apparatus by performingcarrier aggregation using one primary cell and one or a plurality ofsecondary cells, wherein the primary cell is a component carrier of alicensed band, and at least one secondary cell is a component carrier ofan unlicensed band, a frame of the component carrier of the licensedband includes a transmission period of the downlink signal, a frame ofthe component carrier of the unlicensed band includes a transmissionperiod of the downlink signal and a null period during which theterminal apparatus does not transmit a signal, the component carrier ofthe unlicensed band includes a plurality of frame structures, andpriorities are configured for the plurality of frame structures.
 7. Acommunication method used in a base station apparatus that communicateswith a terminal apparatus, the communication method comprising: atransmission step of transmitting a downlink signal to the terminalapparatus by performing carrier aggregation using one primary cell andone or a plurality of secondary cells, wherein the primary cell is acomponent carrier of a licensed band, and at least one secondary cell isa component carrier of an unlicensed band, a frame of the componentcarrier of the licensed band includes a transmission period of thedownlink signal, a frame of the component carrier of the unlicensed bandincludes a transmission period of the downlink signal and a null periodduring which the base station apparatus does not transmit a signal, thecomponent carrier of the unlicensed band includes a plurality of framestructures, and priorities are configured for the plurality of framestructures.
 8. A communication method used in a terminal apparatus thatcommunicates with a base station apparatus, the communication methodcomprising: a reception step of receiving a downlink signal from thebase station apparatus by performing carrier aggregation using oneprimary cell and one or a plurality of secondary cells, wherein theprimary cell is a component carrier of a licensed band, and at least onesecondary cell is a component carrier of an unlicensed band, a frame ofthe component carrier of the licensed band includes a transmissionperiod of the downlink signal, a frame of the component carrier of theunlicensed band includes a transmission period of the downlink signaland a null period during which the terminal apparatus does not transmita signal, the component carrier of the unlicensed band includes aplurality of frame structures, and priorities are configured for theplurality of frame structures.